This invention relates to a chewable tablet containing aspirin in an integral and dispersed combination with a buffering material and the method for producing same. The tablets have use in those applications where aspirin is the prescribed treatment, but its associated undesirable and potentially harmful side effects are wanted to be avoided.
It has long been appreciated that the administration of aspirin with a buffering material has certain distinct advantages. One of these advantages is that the presence of a buffering material serves to increase the rate at which the aspirin is absorbed into the bloodstream. A second benefit is that the buffering material tends to decrease any irritation to the gastrointestinal mucosa that aspirin may cause in some subjects. This is especially true with animals such as dogs whose gastrointestinal tract is particularly sensitive to aspirin irritation.
Although the benefits of the coadministration of aspirin and a buffering material are recognized, the skill in the art for incorporation of these materials in a single dosage form has not developed a thoroughly acceptable product. The principal problem is that aspirin is known to be hydrolyzed to salicylic acid by the alkaline buffering material when moisture is present. This results in an aspirin product with reduced analgesic effectiveness.
U.S. Pat. No. 4,339,428, to Tencza, assigned to Bristol-Myers Co., describes the current level of skill in the art for an aspirin and alkaline tableted combination. Therein it is disclosed that aspirin and buffering material tablets have tried to be made stable by forming the tablets in two layers, one layer containing the aspirin and the other layer containing the buffering material. This has only proven to be relatively successful in providing a stable tablet i.e., one in which the aspirin is not readily hydrolyzed. However, even with the layering of the aspirin and buffering material, the effective aspirin content in a single table is reduced by the hydrolysis surrounding the aspirin alkaline interface.
In addition, such layering greatly increases the production costs of the tablets. Tablets are normally made by direct compression of the tableting products in the die chamber of a tablet press. With layered aspirin and buffer tablets, this requires a two-layered tablet press which is slower than a conventional single-layer machine and requires two separate and distinct compression steps, wherein each layer is separately formed and then joined.
In the administration of medication to animals, there is extreme difficulty in administering tablets and inducing swallowing, and also problems of controlling dosage; it is therefore desirable to have aspirin containing products in a fixed dosage, palatable and chewable form with an undetectable aspirin odor. While many pharmaceutical tablets are designed to be chewed to permit rapid activity in the digestive or circulatory system by increasing the available surface area for absorption of the drug, chewable aspirin buffering material combinations are known to cause an unpleasant oral reaction and leave an unpalatable taste due to chalkiness, grittiness, dryness, and astringent properties of these materials. These palatability and taste problems are also associated with such products administered in non-chewable tablet form, as the tablet tends to dissolve in the mouth before swallowing. Furthermore, in the production of chewable tablets, additional process steps and costs are necessarily encountered. In the production thereof, a disintegrating agent, such as alginic acid, can be added to the pre-tablet mix, and/or reduced compaction temperatures can be employed. However, these techniques cause undesirable mixture adhesion to the die chamber, and cause the tablets to be fragile and bitter.
U.S. Pat. No. 4,327,077, assigned to Life Savers, Inc., describes the current skill in the art to overcome taste and palatability problems. This is primarily accomplished by employing flavorings with the pharmaceuticals. While the flavorings do mask the unpleasant taste, they have not solved any of the associated palatability problems. To overcome palatability problems this same patent discloses a compressed chewable antacid tablet formed by binding the antacid in a fatty material. The fatty material and antacid are mixed and then recrystallized into a powder form and then compacted into a chewable tablet. This chewable tablet is disclosed as disintegrating quickly to a smooth, creamy, pleasant tasting emulsion devoid of grittiness. While the patent discloses a separate embodiment for aspirin and a fatty material, a combined aspirin buffering material tablet is not disclosed and the man skilled in the art would conclude it is not practicable since the disclosed recrystallization into powder form would only serve to integrate the aspirin and alkaline materials causing ultimate hydrolysis and reduction of aspirin into non-analgesic salicylic acid, which is sought to be avoided.
U.S. Pat. No. 4,339,428 discloses the current skill in the art for mixing aspirin and alkaline material in a capsule product wherein a high dosage of aspirin in powder or granulated form is mixed with an alkaline tablet. The capsules are produced by filling them first with the tableted alkaline material, and then adding thereto the aspirin composition in powder or granulated form. However, even with tableting the alkaline material separately from the aspirin, when the products are mixed in the capsule, hydrolysis problems of the aspirin are realized.
Thus, the prior art methods all teach that in a successful aspirin/buffering agent combination, steps must be taken to keep the aspirin and the buffering agent separate at all times until they have been ingested. If intimate contact of the two ingredients in the presence of moisture is allowed to occur to any significant degree, hydrolysis of the aspirin and a significant loss of its analgesic properties will result.